This invention pertains generally to a trigger circuit, more specifically to an arm and gate type trigger circuit for oscilloscopes or various other applications.
Various types of trigger circuits have been proposed for triggering triggerable circuitry or devices such as a ramp signal generator for an oscilloscope. Trigger circuits for an oscilloscope are utilized to stably display an input signal waveform on a cathode-ray tube (CRT) screen.
Arm and gate type trigger circuits have widely been used in modern oscilloscopes. A typical prior art trigger circuit of this type is disclosed in U.S. Pat. No. 3,358,159 to Smith, one embodiment of which is shown in FIG. 1. A pair of triggerable elements, or tunnel diodes are driven by differential outputs of a differential amplifier after a hold-off period. One (arming) tunnel diode is first triggered to its high voltage stable state by one output from the differential amplifier, thereby arming the other (gating) tunnel diode. The other tunnel diode is then triggered to its high voltage stable state by the other output from the differential amplifier to initiate a ramp generator.
Disadvantages of the prior art trigger circuit include the fact that the tunnel diodes are sensitive to the common mode signal, noise, temperature variation, supply voltage fluctuations and that the hysteresis level is not controllable.